Polishing cloth and method of manufacturing semiconductor device using the same

ABSTRACT

A polishing cloth used for a chemical mechanical polishing comprises a base body holding a slurry on the surface and serving to mechanically polish the surface of a target object to be polished. Fine particles soluble in a solvent are dispersed in the base body.

This is a division of application Ser. No. 09/306,758, field May 7,1999, now U.S. Pat. No. 6,337,280.

BACKGROUND OF THE INVENTION

The present invention relates to a polishing cloth used in a chemicalmechanical polishing (CMP).

Recently, a chemical mechanical polishing (CMP) method for flattening asurface of an insulating layer or a wiring layer attracts attentions inthis technical field.

A known polishing cloth used in the CMP method includes “Politex”,(trade name of a polishing cloth manufactured by Rodel Inc.) that doesnot require a pad conditioning treatment (dressing). Politex has a crosssectional shape resembling an arrangement of octopus traps and, thus, isexcellent in its capability of retaining a slurry used for thepolishing, said slurry containing water, SiO₂, Al₂O₃, chemicals(oxidizing agent), etc. Also, Politex has a very flexible surface and,thus, does not impart sharp scratches to the surface of the polishedmaterial.

However, Politex has a very low compression modulus of elasticity, whichis less than 100 MPa, and, thus, is very soft. Therefore, when Politexis used in a flattening process of a target object to be flattened, thepolishing rate is very low and the flatness of;the target object afterthe polishing treatment is not satisfactory.

The known polishing cloth also includes “IC-1000” (trade name of apolishing cloth manufactured by Rodel Inc.). Voids are formed withinIC-1000. Also, IC-1000 has a compression modulus of elasticity of about200 MPa and, thus, is considerably harder than Politex.

In general, a pad conditioning treatment using a diamond conditioningplate is applied to the polishing cloth IC-1000 for polishing asemiconductor wafer. In the pad conditioning treatment, the surfacelayer of the polishing cloth IC-1000 is scratched to form a soft surfacelayer. If the pad conditioning treatment is not applied to IC-1000,IC-100 has a hard surface layer, leading to a low capability ofretaining a slurry and, thus, to a markedly low polishing rate.Naturally, the life of the polishing cloth IC-1000 is determined by thenumber of pad conditioning treatments applied thereto because thesurface layer of the polishing cloth IC-1000 is scratched every time thepad condi-tioning treatment is applied to the polishing cloth IC-1000.

Where the polishing cloth IC-1000 subjected to a pad conditioningtreatment is used for polishing 1000 wafers, the surface layer ofIC-1000 is lost in a thickness of about 850 μm. Where the padconditioning treatment is applied under milder conditions to thepolishing cloth IC-1000 for ensuring a longer life of IC-1000, thepolishing rate is lowered or rendered unstable.

It should be noted that a soft layer having a compression modulus ofelasticity of 10 MPa or less is formed in a thickness of scores ofmicrons in the surface region of the polishing cloth IC-1000 immediatelyafter the pad conditioning treatment. The,particular soft layer impairsthe flatness on the polished surface of the target object.

Further, the soft layer is compressed during the polishing treatment soas to be hardened with progress of the polishing treatment. Since thesurface region is hardened, the scratches generated on the surfaceregion of the polishing cloth IC-1000 are enlarged with progress of thepolishing treatment, though the scratch occurrence on the soft surfaceregion is suppressed immediately after initiation of the polishingtreatment.

As described above, a soft surface layer is formed in the polishingcloth represented by Politex, with the result that the polishing rate islow and the polished target object is not satisfactory in the surfaceflatness, though scratches are not formed on the target object.

On the other hand, the polishing cloth represented by IC-1000 isdefective in that, if a pad conditioning treatment is not applied to thepolishing cloth, many scratches are formed on the target object withprogress of the polishing treatment. If a pad conditioning treatment isapplied to the polishing cloth, however, the surface region of thepolishing cloth is scratched off. Naturally, the polishing cloth isthinned, leading to a short life of the polishing cloth.

Further, if a semiconductor wafer is polished by using the conventionalpolishing cloth for forming, for example, a buried wiring (damascenewiring), dishing or thinning is brought about by an over-polishing so asto generate a so-called “dishing”. The dishing causes a short-circuitingof the wiring formed in an upper layer in the lithography process. Also,the wiring formed on the dished or thinned surface is rendered longer,leading to an increased resistance of the wiring.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention is to provide a polishing cloth thatpermits flattening the surface of a target object at a high accuracy,permits achieving a stable polishing rate, and permits suppressing thescratch occurrence in the target object, and a method of manufacturing asemiconductor device using the particular polishing cloth.

According to an aspect of the present invention, which is intended toachieve the above-noted object, there is provided a polishing clothcomprising a base body holding a slurry on the surface and serving tomechanically polish a surface of a target object to be polished, andfine particles dispersed in the base body and soluble in a solvent.

According to another aspect of the present invention, there is provideda polishing cloth, comprising fine particles soluble in a solvent, and abase body having the fine particles dispersed therein and holding aslurry on the surface, the fine particles being dissolved in the solventwhen a surface of a target object is mechanically polished by thepolishing cloth so as to form concavities on the surface of thepolishing cloth.

According to another aspect of the present invention, there is provideda method of manufacturing a semiconductor device by using a polishingcloth, comprising the steps of forming an insulating film on asubstrate, followed by forming a wiring groove on the substrate throughthe insulating film, forming a metal wiring layer on the substrate andin the wiring groove, burying the metal wiring in the wiring groove, andmechanically polishing the metal wiring buried in the wiring groove witha polishing cloth so as to remove an undesired portion of the metalwiring and, thus, to flatten the surface of the metal wiring, thepolishing cloth comprising a base body holding a slurry on the surfaceand serving to mechanically polish a surface of a target object to bepolished, and fine particles dispersed in the base body and soluble in asolvent.

Further, according to a still another aspect of the present invention,there is provided a method of manufacturing a semiconductor device byusing a polishing cloth, comprising the steps of forming a groove in asubstrate, forming an insulating film on the substrate such that theinsulating film is buried in the groove, and polishing the insulatingfilm by using a polishing cloth so as to remove an undesired portion ofthe insulating film, thus, to flatten the surface of the insulatingfilm, the polishing cloth comprising a base body holding a slurry on thesurface and serving to mechanically polish a surface of a target objectto be polished, and fine particles dispersed in the base body andsoluble in a solvent.

In the polishing cloth of the present invention, fine particles solublein a solvent are dispersed in a base body serving to mechanically polisha target object. During the polishing operation, the fine particlesexposed to the surface of the base body are dissolved in a solvent suchas water to form concavities holding a slurry on the surface of the basebody. It follows that the polishing cloth of the present inventionpermits flattening the surface of the target object highly accurately ata high polishing rate. In addition, the scratch formation can besuppressed on the surface of the polished target object.

In the method of the present invention for manufacturing a semiconductordevice by using the particular polishing cloth, a wiring groove isformed in a substrate, followed by burying a metal wiring in the wiringgroove. Then, the undesired portion of the metal wiring is removed bypolishing with the polishing cloth having fine particles soluble in asolvent dispersed in a base body, thereby improving the quality of thewiring, particularly, a damascene wiring.

Further, the method of the present invention for manufacturing asemiconductor device by using the particular polishing cloth can also beapplied to the case where an oxide film is buried in place of the metalwiring in the wiring groove. In this case, the oxide film is polished bythe polishing cloth to flatten the surface of the oxide filmsatisfactorily.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate presently preferred embodiments ofthe invention, and together with the general description given above andthe detailed description of the preferred embodiments given below, serveto explain the principles of the invention.

FIG. 1 schematically shows the construction of an ideal polishing cloth;

FIG. 2 is a partial cross sectional view showing the construction of apolishing cloth according to a first embodiment of the presentinvention;

FIG. 3 is a cross sectional view partially showing the construction of apolished object used for evaluation of a polishing cloth;

FIG. 4 is a partial cross sectional view showing the construction of apolishing cloth according to a second embodiment of the presentinvention;

FIG. 5 is a cross sectional view of a polishing cloth for explaining theproblem taking place by mutual contact of fine particles within thepolishing cloth;

FIG. 6 is a cross sectional view showing a gist portion in the processof manufacturing a semiconductor device, covering the case where themetal wiring in the buried wiring structure (damascene wiring), which ispolished by the polishing cloth of the present invention, is made ofaluminum;

FIG. 7 is a graph showing a dishing occurrence in the case of polishingthe metal aluminum wiring shown in FIG. 6 with a polishing cloth of thepresent invention in comparison with the prior art;

FIG. 8 is a cross sectional view showing a gist portion in the processof manufacturing a semiconductor device, covering the case where themetal wiring in the buried wiring structure (damascene wiring), which ispolished by the polishing cloth of the present invention, is made ofcopper;

FIG. 9 is a graph showing a dishing occurrence in the case of polishingthe metal copper wiring shown in FIG. 8 with a polishing cloth of thepresent invention in comparison with the prior art;

FIG. 10 is a cross sectional view showing a gist portion in the processof manufacturing a semiconductor device, covering the case where themetal wiring in the buried wiring structure (damascene wiring), which ispolished by the polishing cloth of the present invention, is made oftungsten;

FIG. 11 is a graph showing a dishing occurrence in the case of polishingthe metal tungsten wiring shown in FIG. 10 with a polishing cloth of thepresent invention in comparison with the prior art;

FIG. 12, which is directed to an application of the method of thepresent invention for manufacturing a semiconductor device, is a crosssectional view showing a gist portion in the process of manufacturing asemiconductor device, covering the case where an oxide film buried in agroove formed in a substrate is polished by using a polishing cloth ofthe present invention; and

FIG. 13 is a graph showing that the oxide removal at the same remainingstep/Å is improved in the case of polishing the oxide film shown in FIG.11 with a polishing cloth of the present invention, compared with theprior art.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the present invention will now be described withreference to the accompanying drawings.

Before describing the embodiment of the present invention, theconstruction of a polishing cloth that is ideal in performance will bedescribed with reference to FIG. 1.

A polishing cloth shown in FIG. 1 is considered to meet variousrequirements such as a stable polishing rate, a high flatness in apolished surface of a target object, a capability of suppressing scratchoccurrence, and a long life.

As shown in the drawing, the polishing cloth comprises an inner layer 51and a surface layer 52. For ensuring a good flatness in the polishedsurface of a target object, the inner layer 51 should desirably be hard.Also, the surface layer 52 should desirably be soft for suppressing thescratch occurrence and should desirably be very thin for preventing theflatness of the polished surface from being impaired. Further, thesurface layer 52 should desirably have an appropriately large surfacearea for allowing the surface layer 52 to hold a slurry.

A polishing cloth of the present invention meets all the requirementsnoted above. Specifically, since fine particles are dispersed in a basebody in the polishing cloth of the present invention, the inner regionof the polishing cloth is hard. It should be noted in this connectionthat voids are formed in the conventional polishing cloth IC-1000 asdescribed previously, leading to a hardness lower than that of thepolishing cloth of the present invention.

In the polishing cloth of the present invention, fine particles exposedto the surface are dissolved in a solvent, e.g., water, with the resultthat fine concavities are formed on the surface of the polishing cloth,leading to a large surface area. Of course, a slurry can be heldsatisfactorily on the surface of the polishing cloth. What should alsobe noted is that the irregular surface resulting from formation of fineconcavities makes the surface region softer than the inner region. Sincethe polishing cloth of the present invention has a soft surface, thescratch occurrence can be suppressed.

In another embodiment of the present invention, fine particles coatedwith a material insoluble in water or slurry are dispersed in the basebody. In this case, even if a plurality of fine particles dispersed inthe base body are in mutual contact, all the fine particles in contactwith each other are not dissolved in the solvent such as water. If allthe fine particles in contact with each other are dissolved in asolvent, large concavities are formed in the polishing cloth so as tosoften even the inner layer of the polishing cloth. In the presentinvention, however, the surface coating permits only the fine particlesexposed to the surface to be dissolved in the solvent. Since all thefine particles in contact with each other are not dissolved in thesolvent, large concavities are not formed in the polishing cloth of thepresent invention.

Where the solvent is water or slurry, the fine particles newly exposedto the surface during the polishing operation are dissolved in thesolvent, with the result that deterioration of the polishing performanceis suppressed during the polishing operation.

A high polishing rate can be obtained where the fine particles have adiameter of 5 to 30 μm. Some embodiments of the present invention willnow be described in detail with reference to FIG. 2, et seq.

[First Embodiment]

FIG. 2 is a cross sectional view showing the construction of a polishingcloth 10 for CMP according to a first embodiment of the presentinvention. As shown in the drawing, the polishing cloth 10 comprises abase body 11 made of, for example, polystyrene and about 25% by weightof fine particles, e.g., water-soluble fillers 12 made of cellulose,dispersed in the base body 11.

The base body 11 is hard, and the water-soluble filler 12 is a solidand, thus, is unlikely to be compressed. Therefore, the polishing cloth10 has a compression modulus of elasticity of 10 GPa or more.

Those water-soluble fillers 12 which are exposed to the surface of thepolishing cloth 10 are dissolved in water to form fine concavities so asto increase the surface area of the polishing cloth 10. With increase inthe surface area, the surface region of the polishing cloth 10 issoftened so as to prevent scratches from being formed on the polishedsurface of the target object. In addition, the slurry can be retainedefficiently by the polishing cloth 10.

The density and depth of the concavities formed on the surface of thepolishing cloth 10 can be controlled easily by controlling the diameterand the mixing ratio of the water-soluble fillers 12. In other words,the conditions of the surface region such as the thickness and softnesscan be controlled easily by controlling the diameter and the mixingratio of the water-soluble fillers 12.

Table 1 shows the polishing rate and the scratch occurrence, coveringthe case where an aluminum material containing 0.5% of copper waspolished by the polishing cloth 10 of the present invention as well asby the conventional polishing cloths of Politex and IC-1000:

TABLE 1 Polishing Polishing Scratch cloth Conditioning rate occurrencePolitex none 230 nm/min none IC-1000 none  60 nm/min large scratchIC-1000 scratch 210 nm/min small scratch Polishing none 205 nm/min nonecloth of present invention Polishing scratch 310 nm/min none cloth ofpresent invention

In the case of the conventional polishing cloth of IC-1000, thepolishing rate was 60 nm/min where the conditioning treatment was notapplied thereto, which was markedly lower than the polishing rate of 210nm/min where the conditioning treatment was applied thereto. It isconsidered reasonable to understand that, if a conditioning treatment isnot applied, the surface layer of the polishing cloth IC-1000 wasincapable of sufficiently retaining the slurry, leading to the markedlylow polishing rate.

On the other hand, the polishing cloth of the present invention achieveda high polishing rate of 205 nm/min even if the conditioning treatmentwas not applied thereto. Clearly, the water-soluble fillers exposed tothe surface of the polishing cloth were dissolved in water (slurry) toform fine concavities on the surface of the polishing cloth. As aresult, the surface area of the polishing cloth was increased and theslurry was retained sufficiently on the surface of the polishing cloth,leading to the high polishing rate.

It should also be noted that the polishing cloth of the presentinvention was found to be stable in the polishing rate. It should benoted in this connection that the water-soluble fillers 12 are newlyexposed to the surface with progress in the abrasion of the surfacelayer of the base body 11 during the polishing operation. Naturally, thenewly exposed fillers 12 are dissolved in the slurry to form newconcavities on the surface of the polishing cloth 10, with the resultthat the polishing rate is kept stable, as pointed out above.

Further, where a conditioning treatment was applied to the polishingcloth 10 of the present invention, the polishing rate was found to bevery high, i.e., 310 nm/min, which is markedly higher than the polishingrate in the case where the conditioning treatment was not applied to thepolishing cloth 10 of the present invention or the polishing rateachieved by the conventional polishing plates of Politex and IC-1000.

A dishing amount was evaluated by using a semiconductor structure shownin FIG. 3 as a sample to be polished. As shown in the drawing, thesemicon-ductor structure consisted of a silicon substrate 21, a siliconoxide film 22 formed on the silicon substrate 21 and having recesses,and an aluminum film 23 formed on the entire surface of the siliconoxide film 22. The aluminum film 23 was 800 nm thick, and the siliconoxide film 22 was 700 nm thick. Further, each of the recesses formed inthe silicon oxide film 22 was 400 nm deep. A width A of the recess and adistance B between the two adjacent recesses were set to meet therelationship: A/(A+B)=0.7. The dishing amount was evaluated for thecases where the width A of the recess was set at 10 μm and 100 μm.

To be more specific, the aluminum film 23 was polished until thepolished surface reached a curve 23 b so as to evaluate the dishingamount. Table 2 shows the results of the evaluation:

TABLE 2 Width of Width of Polishing wiring wiring cloth Conditioning (A= 10 μm) (A = 100 μm) Politex none 160 nm >350 nm IC-1000 none 200 nm  250 nm IC-1000 scratch  80 nm   210 nm Polishing none  8 nm    40 nmcloth of present invention Polishing scratch  20 nm    80 nm cloth ofpresent invention

In the case of using the conventional polishing cloth of Politex, whichis a very soft polishing cloth, the dishing amount was very large, i.e.,160 nm in the case where the width of the wiring was only 10 nm, andmore than 350 nm in the case where the width of the wiring was 100 nm.

In the case of using the conventional polishing cloth of IC-1000 towhich a conditioning treatment was applied, the dishing amount wassuppressed to 80 nm (A=10 μm) and 210 nm (A=100 nm), which are smallerthan those in the case of using Politex. However, these values aremarkedly larger than those in the case of using the polishing cloth ofthe present invention. A soft surface layer is formed on the polishingcloth IC-1000 by the conditioning treatment so as to give an adverseeffect to the flatness of the polished surface. Therefore, it appearsreasonable to understand that the dishing amount is diminished in thecase where a conditioning treatment is not applied to IC-1000. However,the dishing amount in the case where a conditioning treatment was notapplied to IC-1000 was found to be 200 nm (A=10 μm) and 250 nm (A=100μm), which are clearly larger than those in the case where theconditioning treatment was applied.

It should be noted in this connection that, if a conditioning treatmentis not applied, a deep scratch deeper than 20 nm is formed on thesurface of the aluminum film, and the aluminum film is eroded such thatthe scratch is enlarged, leading to the large dishing amount as pointedout above.

On the other hand, in the case of using the polishing cloth 10 of thepresent invention to which a conditioning treatment was not applied, thedishing amount was found to be only 8 nm in the case where the width Aof the recess was set at 10 μm and to be only 40 nm in the case wherethe width A of the recess was set at 100 μm. Clearly, the polishingcloth of the present invention permits markedly improving the dishingamount.

To reiterate, the polishing cloth 10 of the present invention comprisesthe very hard base body 11 having a compression modulus of elasticity of10 GPa. In addition, the polishing cloth 10 has a soft surface layer. Itfollows that scratches are not generated on the polished surface of thetarget object. Also, a slurry is held sufficiently on the soft surfaceof the polishing cloth. Further, the soft surface layer is controlled tobe very thin. These conditions are considered to have diminished thedishing amount in the case of using the polishing cloth of the presentinvention.

Incidentally, the dishing amount was found to be 20 nm (A=10 μm) and 80nm (A=100 μm) in the case of using the polishing cloth 10 of the presentinvention to which a conditioning treatment was applied. Theconditioning treatment is considered to have further softened the softsurface layer and/or to have increased the thickness of the soft surfacelayer so as to increase the dishing amount.

A polishing rate of an aluminum film was evaluated by varying thediameter of the water-soluble filler 12. In each of the test cases, thepolishing cloth was prepared by setting the concentration of thewater-soluble fillers at 25% by weight. Table 3 shows the results:

TABLE 3 Filler diameter Polishing rate (nm/min)  1 μm  420  5 μm 2050 10 μm 2200  30 μm 1400  50 μm  950 100 μm  800

Table 3 clearly shows that the polishing rate is dependent on thediameter of the water-soluble filler 12. Where the filler diameter wasset at 1 μm, a large number of scratches were generated on the polishedsurface of the aluminum film. It should be noted that the concavitiesformed on the surface of the polishing plate are unduly small where thefiller diameter is 1 μm, resulting in failure to form a soft surfacelayer on the polishing cloth 10. Also, where the concavities formed onthe surface are unduly small, the polishing cloth fails to retain theslurry sufficiently. As a result, numerous scratches were generated onthe polished surface of the aluminum film.

On the other hand, the polishing rate was low in the case where thefiller diameter was set at 50 μm or 100 μm. The low polishing rate isconsidered to have been caused by the phenomenon that concavities formedon the surface of the polishing cloth were unduly large. Theexperimental data shown in Table 3 clearly support that the diameter ofthe water-soluble filler should desirably fall within a range of betweenabout 5 μm and 30 μm.

As described above, the polishing cloth of the present inventioncomprises a soft surface layer having a large number of concavitiesformed therein and an inner layer consisting of a base body and a largenumber of water-soluble fillers dispersed in the base body. Theparticular construction of the polishing cloth produces prominenteffects. To reiterate, the soft surface layer including a large numberof concavities permits improving the polishing rate and suppressing thescratch formation. At the same time, the hard inner layer permitsimproving the flatness of the polished surface of the target object.

What should also be noted is that, even if the surface layer of the basebody is abraded during the polishing treatment, other water-solublefillers are newly exposed to the surface of the polishing cloth so as tobe dissolved in water or slurry. It follows that a soft surface layer iskept formed on the polishing cloth, making it possible to obtain astable polishing rate.

An additional feature of the present invention to be noted is that,since a soft surface layer is formed, it is substantially unnecessary toapply a conditioning treatment to the polishing cloth so as to increasethe life of the polishing cloth.

(Second Embodiment)

FIG. 4 is a cross sectional view showing the construction of a polishingcloth according to a second embodiment of the present invention. Thosemembers of the polishing cloth shown in FIG. 4 which are equal to thoseshown in FIG. 2 are denoted by the same reference numerals so as to omitan overlapping description.

The polishing cloth of the second embodiment is featured in that acoating layer 31 made of a material insoluble in water (slurry) isformed to cover the outer surface of the water-soluble filler 12.

Where a large amount of the water-soluble filler is dispersed in thebase body, the filler particles tend to be brought into mutual contactwithin the base body with a high probability. If the polishing cloth inwhich filler particles are in mutual contact is brought into contactwith water, a large and deep concavity 41 is formed, as shown in FIG. 5.

In the second embodiment of the present invention, however, all thewater-soluble fillers 12, which are in mutual contact, are not dissolvedin the solvent because of the presence of the coating layer 31.Naturally, the concavity formed on the surface does not extend deep intothe base body, making it possible to prevent the compression modulus ofelasticity of the polishing cloth from being lowered.

The present invention is not limited to the embodiments described above.For example, in each of the embodiments described above, the base bodyis formed of polystyrene, and the water-soluble filler is formed ofcellulose. However, other materials can also be used for forming thesebase bodies and the water-soluble fillers.

It is also possible to disperse a liquid material into the base body inplace of the solid water-soluble fillers. The liquid material, which iscertainly softer than a solid material, is sufficiently hard, comparedwith a gaseous material, making it possible to use a liquid material inplace of the water-soluble filler. Of course, the liquid materialexposed to the surface of the base body flows out of the base body so asto form concavities in the regions in which the liquid material wassealed previously. It follows that the liquid material dispersed in thebase body produces an effect similar to that produced by the solidwater-soluble filler.

In the embodiments described above, the fine particles dispersed in thebase body are soluble in water. However, it is also possible to dispersefine particles that are soluble in a solvent other than water in thebase body. It suffices to spray a solvent capable of dissolving the fineparticles against the surface of the polishing cloth before performingthe polishing treatment so as to dissolve the fine particles dispersedin the base body so as to form concavities on the surface of thepolishing cloth.

A method of manufacturing a semiconductor device having a damascenewiring structure involving a wiring groove will now be described. Thepolishing cloth of the present invention described above is employed inthe manufacture of the particular semiconductor device.

Specifically, FIG. 6 is a partial cross sectional view showing adamascene wiring structure in which an Al wiring 3 was buried in awiring groove 2 formed in a SiO₂ substrate 1. The wiring groove 2 had adepth of 4,000 Å and a width of 100 μm. Also, the thickness of the Allayer included in the Al wiring 3 was 8,000 Å before the polishingoperation.

It should be noted that the Al wiring 3 is buried in the wiring groove2, and the surface of the Al wiring 3 is polished by the polishing clothof the present invention. In this case, the Al wiring 3 is over-polishedsuch that the upper surface of the Al wiring 3 is positioned within thewiring groove 2 that is lower than the upper surface of the SiO₂substrate 1 so as to bring about a so-called “dishing” or “thinning”. Asa result, a dishing is brought about.

In this embodiment, the flatness of the polished surface of the Alwiring 3 was evaluated under a load of 300 g/cm² and the rotating speedof the table and the carrier set at 50 rpm. The scratches formed on theAl wiring 3 buried in the wiring groove 2 were evaluated by KLA, withthe result that 42,328 scratches/wafer were observed in the case ofusing the conventional polishing cloth of IC-100 in contrast to only 320scratches/wafer in the case of using the polishing cloth of the presentinvention.

FIG. 7 is a graph showing that the polishing cloth of the presentinvention is markedly superior to the conventional polishing cloth inthe effect of suppressing the dishing occurrence. To be more specific,the number of dishings that took place in the case of polishing the Alwiring 3 with the conventional polishing cloth of IC-1000 exceeded 3,500dishings (Å) when the over-polishing reached 60% of the depth of thewiring groove 2, as seen from the dotted line shown in FIG. 7.

On the other hand, a slurry prepared by dispersing in water 3% by weightof Al₂O₃, 1% by weight of (NH₄)₂S₂O₈ and 0.02% of benzotriazole wasretained on the surface of the polishing cloth of the present inventionhaving fine particles dispersed in a base body. In the case of polishingthe surface of the Al wiring 3 with the polishing cloth of the presentinvention noted above, the number of dishings occurring on the surfaceof the polished Al wiring 3 scarcely increased even when theover-polishing reached 60% of the depth of the wiring groove 2 as seenfrom the solid line shown in FIG. 7. The experimental data clearlysupport that the quality and the characteristics of the Al wiring 3 wereimproved by the polishing treatment in the case of using the polishingcloth of the present invention. In other words, the wiring was formedsatisfactorily.

FIG. 8 is a partial cross sectional view showing a damascene wiringstructure in which an Cu wiring 4 was buried in a wiring groove 2 formedin a SiO₂ substrate 1. The wiring groove 2 had a depth of 4,000 Å and awidth of 100 μm. Also, the thickness of the Cu layer included in the Cuwiring 4 was 8,000 Å before the polishing operation.

FIG. 9 is a graph showing that the polishing cloth of the presentinvention is markedly superior to the conventional polishing cloth inthe effect of suppressing the dishing occurrence. To be more specific,the number of dishings that took place in the case of polishing the Cuwiring 4 with the conventional polishing cloth of IC-1000 approached3,500 dishings (Å) when the over-polishing reached 60% of the depth ofthe wiring groove 2, as seen from the dotted line shown in FIG. 9.

On the other hand, a slurry prepared by dispersing in water 1% by weightof Al₂O₃, 1% by weight of (NH₄)₂S₂O₈ and 0.05% of benzotriazole wasretained on the surface of the polishing cloth of the present inventionhaving fine particles dispersed in a base body. In the case of polishingthe surface of the Cu wiring 4 with the polishing cloth of the presentinvention noted above, the number of dishings occurring on the surfaceof the polished Cu wiring 4 increased only slightly even when theover-polishing reached 60% of the depth of the wiring groove 2 as seenfrom the solid line shown in FIG. 9.

FIG. 10 is a partial cross sectional view showing a damascene wiringstructure in which a W wiring 5 was buried in a wiring groove 2 formedin a SiO₂ substrate 1. The wiring groove 2 had a depth of 4,000 Å and awidth of 100 μm. Also, the thickness of the W layer included in the Wwiring 5 was 8,000 Å before the polishing operation.

FIG. 11 is a graph showing that the polishing cloth of the presentinvention is markedly superior to the conventional polishing cloth inthe effect of suppressing the dishing occurrence. To be more specific,the number of dishings that took place in the case of polishing the Wwiring 5 with the conventional polishing cloth of IC-1000 exceeded 3,500dishings (Å) when the over-polishing reached 60% of the depth of thewiring groove 2, as seen from the dotted line shown in FIG. 11.

On the other hand, a slurry prepared by dispersing in water 3% by weightof Al₂O₃ and 5% by weight of Fe(NO₃)₃ was retained on the surface of thepolishing cloth of the present invention having fine particles dispersedin a base body. In the case of polishing the surface of the W wiring 5with the polishing cloth of the present invention noted above, thenumber of dishings occurring on the surface of the polished W wiring 5increased only slightly even when the over-polishing reached 60% of thedepth of the wiring groove 2 as seen from the solid line shown in FIG.11.

An additional experiment was conducted as another embodiment of thepresent invention. In this experiment, an oxide film 6 having athickness of 14,000 Å was formed on a Si substrate 1 having a wiringgroove 2 formed on the surface in a depth of 7,000 Å and a width of 100μm, as shown in FIG. 12. The upper surface of the oxide film 6 thusformed was polished with the polishing cloth of the present invention.The slurry used in the polishing step was prepared by diluting SC-1manufactured by Cabot Inc. with pure water twice as much as SC-1.

The-experimental data are shown in a graph of FIG. 13 in terms of therelationship between the remaining step (Å) and the oxide removal (Å). Adotted line shown in FIG. 13 represent the polishing with theconventional polishing cloth of IC-1000. On the other hand, the solidline in FIG. 13 represents the polishing with the polishing cloth of thepresent invention. As apparent from FIG. 13, the solid line representingthe use of the polishing cloth of the present invention is closer to anideal curve than the dotted line representing the use of theconventional polishing cloth of IC-1000. It follows that the polishingcloth of the present invention permits flattening the surface of anoxide film more uniformly than the conventional polishing cloth ofIC-1000.

The present invention can be worked in variously modified fashionswithin the technical scope of the present invention.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

What is claimed is:
 1. A polishing cloth, comprising: a base bodyholding a slurry on a surface thereof and serving to mechanically polisha surface of a target object to be polished; and fine particlesdispersed in said base body, said fine particles having a solid coresoluble in a solvent in said slurry and coating layers insoluble by saidsolvent in said slurry formed on outer surfaces of said solid core offine particles.
 2. The polishing cloth according to claim 1, wherein asurface layer of said base body includes fine concavities resulting fromdissolution of said fine particles in a solvent.
 3. The polishing clothaccording to claim 1, wherein voids are not present inside said basebody.
 4. The polishing cloth according to claim 1, wherein at least oneof SiO₂ and Al₂O₃ and an oxidizing agent are included in said slurry. 5.The polishing cloth according to claim 1, wherein said fine particleshave a particle diameter of 5 to 30 μm.
 6. A polishing cloth,comprising: fine particles being a soluble solid in a solvent in aslurry, said fine particles having a particle diameter of 5 μm or more;and a base body having said fine particles dispersed therein and holdingsaid slurry on a surface thereof, said fine particles being dissolved insaid solvent in said slurry when a surface of a target object ismechanically polished by said polishing cloth so as to form concavitiesin a surface layer of said polishing cloth.
 7. The polishing clothaccording to claim 6, wherein a coating layer insoluble in said solventin said slurry is formed to cover the outer surfaces of said fineparticles.
 8. The polishing cloth according to claim 6, wherein voidsare not present inside said base body.
 9. The polishing cloth accordingto claim 6, wherein at least one of SiO₂and Al₂O₃ and an oxidizing agentare included in said slurry.
 10. The polishing cloth according to claim6, wherein said fine particles have a particle diameter of 30 μm orless.